CombiCard is a Planning Poker app, designed to be used during Planning Poker sessions.
Planning Poker is a way of estimating the relative size of a piece of work, via consensus. It is typically used during Agile (particularly Scum) but can be used as a practice in its own right.
Items are "sized" i.e. given a single overall value/score that represents their relative size to each other, in terms of:

likely effort

complexity

and possibly how well understood it is.

Planning Poker is usually used in conjunction with other agile practices but can be used in isolation.